It is often necessary to establish a localized electrical contact with the external body surface of a living subject. Such contact is typically achieved by the use of electrically conductive electrodes having extended surface areas placed in electrical contact with a desired portion of an external body surface through an intermediate electrode gel, liquid or other preparation designed to ensure good and continuous electrical contact between the living body surface and the conductive electrode surface. Such electrical connections to living subjects are now commonly required for therapeutic and diagnostic applications in both medical and veterinary usage. For example, electro-therapeutic stimulation has now been recognized to promote the healing of bones and other body tissues and/or to have other advantageous physiological effects. Many diagnostic techniques (e.g., electrocardiograms) also require electrical connections to body surfaces so as to monitor electrical body surface potentials.
Medical research has applied advanced temperature measurement techniques such as infrared thermography and liquid crystal films to diagnose and identify various forms of vascular diseases and tumors. Since temperature is an indicator of circulatory function, techniques have been developed to measure the effects of nerve blocking drugs on the circulatory system by measuring temperature. In addition to diagnostic applications, temperature measuring devices have been used in medicine to locate everything from veins to placental attachment sites. A recent invention using liquid cyrstals, U.S. Pat. No. 4,378,808, can be used to detect unwanted infusion of fluids into tissue when an IV fails.
U.S. Pat. No. 4,213,463 discloses a body electrode with a physically movable visual indicator comprising a flap imprinted with areas of green and red, supposedly designed to ensure optimal parallel positioning and electrical current distribution. U.S. Pat. No. 4,016,761, discloses a probe using liquid crystals and optical fibers for measuring temperature changes of tissue while the tissue is being irradiated with microwaves. U.S. Pat. No. 3,951,133 employs tin foil as a liquid crystal substrate but there is no suggestion that the tin foil might be utilized as an electrode.
Temperature measurement has also been applied for therapeutic use in the field of bio-feedback. A variable signal tone, light or meter provides the patient with a feedback signal that relates to the patient's skin temperature. The patient is trained to respond to this type of feedback by modifying his temperature and behavior.
Electrotherapy devices have heretofor employed meters, lights, or tone generators to indicate the voltage/current that is applied to a patient's electrodes (or to the treatment coils in the case of pulsed magnetic field devices). Lights and meters have also been used to indicate the current that passes through a patient. These conventional techniques measure some form of electricity in order to show that a signal is applied to or present in the patient. They do not, however, indicate the quality of the physiological link between the electrotherapy device and the patient. There is a critical need for an electrotherapy device to conveniently and accurately monitor the quality of the electrical connection and the quality of the resulting physiological effects during the electrotherapy process.
In addition to temperature changes that occur due to disease and the body's response to drugs, temperature changes that result from various forms of electrotherapy have been studied. Several studies have shown that skin temperature will rise in response to electrical signals produced by certain transcutaneous electrical nerve stimulators (TENS) that are applied to control pain. Other types of electrotherapy devices cause skin temperature to drop while achieving inflammation reduction and tissue repair. Improved local circulation by increased vascularization, or alternating vaso-dilation and vaso-constriction will be indicated by a rise in temperature.